1. Field of the Invention
The present invention relates to an imaging apparatus such as a single-lens reflex camera, and more particularly to an imaging apparatus including an element transmittance and reflectance of which can be changed.
2. Description of the Related Art
A conventional single-lens reflex camera includes a structure in which a reflection mirror for guiding incident light to an optical viewfinder to confirm an object is arranged in an imaging optical path, and is caused to retreat to focus the incident light onto a film or an image sensor during image capturing. In a digital camera using the image sensor, live view for displaying an object image on a display monitor to confirm an object can be performed so that not only a still image but also a moving image can be recorded in a live view state. However, the reflection mirror is required to retreat from the imaging optical path to achieve the live view state. Therefore, the object cannot be confirmed by the optical viewfinder.
Japanese Patent Application Laid-Open No. 10-39408 discusses a structure in which a reflection mirror is a semi-transparent mirror, and an object image is incident on both an optical viewfinder and an image sensor, respectively, after being separated into an optical viewfinder image and a captured image.
However, an amount of light is divided, so that the optical viewfinder image becomes dark, and the captured image is required to be intensified because it is insufficiently exposed, degrading the object image.
To solve such a problem, Japanese Patent Application Laid-Open No. 2009-180822 discusses a method, using a variable transmittance element as a reflection mirror, for increasing reflectance of the reflection mirror to make an optical viewfinder image easy to see when confirming the optical viewfinder image and increasing transmittance of the reflection mirror when capturing an image to prevent a decrease in an amount of light in the captured image.
In an imaging apparatus such as a single-lens reflex camera, a purpose of changing a diaphragm aperture includes making an amount of exposure of a captured image appropriate and controlling a depth of field.
When the depth of field is optionally set, for example, when an aperture value is set large, to increase the depth of field to widen an in-focus range, the amount of exposure is insufficient. Therefore, a shutter exposure time is lengthened, and sensitivity of the image sensor is increased.
If a diaphragm aperture of a lens is changed in a live view state or during moving image capturing, an optical viewfinder can also observe imaging light even during exposure in a camera using the semi-transparent mirror, as discussed in Japanese Patent Application Laid-Open No. 10-39408. However, change in an amount of light incident on the optical viewfinder occurs due to a diaphragm operation, so that a problem occurs in such a way that a photographer cannot confirm whether an image can be captured under an appropriate exposure condition.
If the variable transmittance element, as discussed in Japanese Patent Application Laid-Open No. 2009-180822, is used as a reflection mirror in a single-lens reflex camera, an amount of light incident on an optical viewfinder can be increased until a still image is captured, and an amount of light incident on an image sensor can be increased only the moment that the still image is captured. In this way, if control is thus performed on an imaging sequence, an uncomfortable feeling to be given to a photographer can be reduced. However, when a diaphragm aperture of a lens is changed in a live view state or during moving image capturing, not only the amount of the light incident on the image sensor but also the amount of light incident on the optical viewfinder changes. Therefore, the photographer who is looking into the optical viewfinder may be made to have an uncomfortable feeling.
More specifically, even if a captured image is appropriately controlled for the aperture value by controlling a shutter and the image sensor, the optical viewfinder image changes depending on the aperture value. If the aperture value is large, the object image becomes dark, so that there is a problem in which the photographer does not easily recognize the object.